The disclosed invention is a fluid pump having an easily replaceable pumping element that is free of bearings, frictional contact or rotating parts in the flow path, and that is also free of bearings, flexing seals or apertures leading to the exterior, except for the inlet and the outlet of the pumping element. While the new pump will be advantageous in many applications where leakage, fluid contamination and damage by or to the fluid are objectionable, such as pumping pharmaceuticals and biological and sanitary fluids, a major application will be as a blood pump for circulatory assist and also for cardiopulmonary bypass.
There has been an increasing interest in continuous, rotary blood pumps for circulatory assist and circulation maintenance, to alleviate problems identified with displacement types of ventricular assist devices such as infection, thrombosts and control. There are also, however, mechanical problems with existing centrifugal (and other rotary) pumps, such as infection through shaft seal, possible seal leakage, thrombosts and blood injury in bearings.
The fact that such problems are still prevalent with rotary blood pumps, in spite of the large number of different developments that have taken place in recent years is attested to by reference to them in a number of papers presented at an International Workshop on Rotary Blood Pumps held in Baden, Austria Sep. 9-11, 1991. It was indicated that lack of a long-lived bearing is the principal obstacle to the use of a continuous rotary pump as an implanted assist device. It was also found that bearing seals in rotary blood pumps were apt to fall when immersed in blood. If there were no seal for a rotating bearing in a rotary blood pump, such problems would not exist.
It was also stated that blood leakage and thrombus formation about bearing or shaft seals still limit the clinical usage of centrifugal pumps, which require seals between the blood and bearings and actuators, and that commercially available disposable blood pumps can only be used on a patient for 48 hours before being replaced. The objective is for the development of a centrifugal blood pump which can provide over two weeks of continuous operation with an Inexpensive replaceable pumping element.
No practical, commercially available pump, based on oscillation of a centrifugal impeller within a replaceable pumping element suitable for blood pumping, and being free of bearings, flexing seals or external apertures is known to the applicant. U.S. Pat. No. 3,148,970 entitled "Method and Apparatus for Pumping Fluids by Oscillatory Impeller Action" and dated Aug. 11, 1964 discloses a separate oscillating pump driven by an oscillating electric motor through an external shaft that requires bearings and seals, and in which the system has ". . . longitudinally adjacent portions simultaneously torsionally elastically deformable in reverse directions about and with reference to an intermediate neutral portion . . ." The system disclosed is not adaptable for the pumping element to be contained in a sealed housing. U.S. Pat. Nos. 4,595,338 and 4,684,828 show bearing less fans using piezoelectric blades and U.S. Pat. No. 8,165,086 discloses an articulated fish-tail type of oscillating propeller for boats.
There is an evident need for an extracorporeal blood pump with a relatively long-lived, replaceable and inexpensive pumping element that has no bearings or frictional contacts within the element that could damage the blood, and no external apertures that could be paths for leakage or contamination.